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Jazz and modbus

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I'm using JAZZ JZ20-R31 as a master to comunicate via modbus.


Is there possibility to use another master device on the same line which would read data from JAZZ?


Requests from one master would be about a minute interval and around 15minutes from the other, so there would be little chance for interference.


I know this isn't the right way to do this, but just curious... Is it possible to do this or is JAZZ somehow "locked" and unable to be read by someone while JAZZ itself is operating as a master?


Thank you,




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  • 8 months later...
On 2-5-2016 at 7:19 AM, Joe Tauser said:

It can also be a slave.  Put a SCAN/EX block in.


Joe T.

Hello Joe,

In my U90 Ladder, i cannot find the scan/EX block.
Will this be a special function, where I store a specific number in SI140?

Reason i ask is because i'm trying to communicate via RS485 between my V350 master to a JZ10-11-T40 slave.
Write from master to slave works fine, but i cannot read from the slave.

Thanks in advance,

Jos Koopman

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  • MVP 2023

I wasn't thinking when I answered that.  My answer was for a Vision.

I checked the Help and special Function 599 stored to SI 140 allows Slave functionality.  I must admit I've never talked to a Jazz as a slave, so I am most curious how well this works.

Open the U90 Help and Search for Modbus.  The value 599 isn't very well documented - it's in the table Function description under the RTU Modbus Configuration topic.

Let me know your results.

Joe T.

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Hi Joe,

I did find the 599 command. Explanation i found was that with 599 the serial port still works if the RS485 is unplugged, with 600 this is not the case.

I tried with 599, also 600. Both without success.

Also tried to set the Jazz as master and set the vision as slave with the scan/EX block.

But also no success.  

Further when i watched the video tutorial for the vision modbus, they explained that  the number of total sessions should ideally match the number of acknowledgements. In my case i have zero acknowledgements, even when the write function is successful to the slave. So looks like there is absolutely nothing coming back from the jazz to the vision.
maybe I'm overlooking something in the vision controller.

In the jazz, i first do a comport init, (SI141-145 = 9600/8/2/2/100), then  310 stored in SI140,.
Next net is the modbus config with 599 in SI 140 (SI141-145 = 2/100/3/2/9600)

I tried storing 599 in SI140 various ways after this.
Every 10 seconds a pulse, on every scan of the ladder, but without success.

On the forum i also found an old tread, where Apollas had the same problem with receiving but not sending.
He also replied that he did get it working, but could not remember how he did it.
He offered to send his  codes. Maybe that will help me.
He also mentioned SB134.

And in the example from Unitronics there is 0 stored in SB64. But that also did not change anything for me.

I'll let you know once i make some progress.




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